Method of and apparatus for detecting vital functions of living bodies

ABSTRACT

An apparatus for detecting vital functions of living bodies by means of electromagnetic signals includes a receiving device for electromagnetic signals. The receiving device for electromagnetic signals includes a device for obtaining frequency components that are characteristic of living bodies, out of received electromagnetic signals. The receiving device includes a direct demodulator that has a non-linear current/voltage characteristic that is frequency-selective for demodulation of frequency components that are characteristic of living bodies.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention concerns an apparatus for detecting vital functions ofliving bodies, and more particularly to an apparatus for detecting vitalfunctions of living bodies by means of electromagnetic signals.

The inventors found that living bodies and therefore also human livingbodies surprisingly influence high-frequency electromagnetic signals byvirtue of their most important vital functions, that is to say theirheartbeat and their respiration activity.

Those vital functions generally take place within known frequencyranges, which with the human heart rate can be from about 0.5 through3.4 Hz and normally are about 1 through 2 Hz and in the case ofrespiration can extend between 0.1 and 1.5 Hz. That definescharacteristic frequency ranges. Upon the reception and recording ofelectromagnetic signals those frequency ranges are visible when peopleare in the reception region. In addition it is possible to provideinformation about the number of people located, on the basis of receivedand also processed signals. In that respect, use is made of theprinciple of biological variety and specificity, on the basis of whichthe heart and respiration frequency patterns of different people differ.For four or more people however, it is generally no longer possibleclearly to distinguish between the number of people by virtue of thefrequency superimposition of the respective frequencies. As from thatnumber of people it is then only possible to provide the informationthat: there are at least four people present.

In any event a frequency range of 0.01 through 10 Hz includes allfrequencies which are of interest in terms of the vital functions of ahuman body.

What was surprising was the realisation that even without emittedtransmission power, just the receiver device together with the devicefor obtaining the frequency components which are characteristic ofliving bodies the inventors were in a position to provide the desiredidentification effect for the vital functions.

This means that the presence of a living body, at least in the vicinityof the receiver device, already results in detectable signal componentsin the specified frequency ranges, without in that respect the need forthrough-radiation with a carrier signal.

With the receiver device for electromagnetic signals and the device forobtaining frequency components which are characteristic in respect ofliving bodies, without additional emitted signals, the inventors werealready in a position of reliably detecting living bodies at up to morethan 3 meters distance or approximately the distance of the storey of abuilding.

In the simplest embodiment of the invention the direct demodulatordescribed hereinafter, in the form of a diode direct receiver forreceiving the frequency components which are characteristic in respectof living bodies, was already sufficient.

In addition transmitters were later used, with which through-radiationof the detection area was effected, and reflected, transmitted orscattered radiation was received, the investigation thereof forpronounced frequency components providing the proof of the presence ofliving bodies.

So that electromagnetic radiation can still be received through densedebris, even at some distance, frequencies of the electromagneticradiation of some hundred megahertz to about 10 gigahertz were used,which ensured a high depth of penetration.

That radiation experienced phase modulation which added side bandsdisplaced by some Hertz to the high-frequency carrier signal. Withconventional reception procedures, detection of frequency bands whichare so close together would have required short term-stable oscillatorswith deviations of less than 10⁻¹², which hitherto was considered to beunattainable at reasonable cost. That problem is made more acute by thelow levels of received signal powers.

Some of the advantages of the embodiments described herein are discussedhereinafter.

The use of known phase modulators initially appears obvious. Homodyne,heterodyne and PLL (Phase Locked Loop) methods and the excitation of theflanks of a local oscillation circuit are known. It has been foundhowever that none of the foregoing processes was capable of supplyingthe desired results at an expenditure that was reasonable. It was onlythe use of a direct demodulator which permits direct separation of themodulation frequency from the modulated frequency, that leads to thedesired results. It is assumed however that, with suitable apparatusexpenditure and improved circuit arrangements, the foregoing methods canbe used in accordance with the present invention.

With a component with a non-linear current/voltage characteristic as thefrequency-selective element, it was possible to provide inexpensivelyand reliably for demodulation of the frequency components which are ofinterest. A diode, a bipolar or a field effect transistor could besuccessfully used as the element with a non-linear characteristic.

Those components are both inexpensively obtainable and also non-criticalin regard to their use. The optimum working range of those components offrom about 100 kHz to 200 MHz could be used at higher receptionfrequencies by means of a frequency conversion device connected upstreamof the demodulator. Although that frequency conversion device addedtolerable distortion in the time region to the signal, it did howeversuperimpose only a slight amount of additional noise.

The signal to be received could be raised with a transmitter device fortransmitting an electromagnetic carrier signal at a fixed frequency;however a very high level of attention had to be paid to the stabilityof the carrier frequency in order to exclude undesirable modulationeffects in the frequency range which is of interest. A simplequartz-stabilised analog transmission circuit with an oscillator circuitof high quality surprisingly showed itself to be a suitable oscillator,after an adequate transient or build-up time.

The method and the apparatus according to the invention can also be usedfor object monitoring and/or safeguarding. The specific embodimentsshow, at a later point in this description, static monitoringarrangements.

The use of an analog sampling filter, unlike high-frequency digitalfilters, did not exhibit any detrimental additional frequency componentsand crucially contributed to the quality of the signal obtained.Additional undesirable signal components such as for example noise andsuperimposed interference were prevented by limiting the band width ofthe electromagnetic signal prior to the sampling operation and prior toA/D-conversion to high frequencies.

The use of an analog high pass filter for preventing low-frequencycomponents in respect of the frequency-dependent 1/f-noise of thetransmission oscillator and internal structural units was alsoimportant.

The unexpectedly good operation of the apparatus according to theinvention and the method according to the invention also permits usethereof in many areas.

People who are in danger of committing suicide can be monitored inpsychiatry or in places of detention, without requiring constantinspection by personnel who are in charge of such people.

The invention is described in detail hereinafter by means of embodimentsgiven by way of example with reference to the accompanying drawings inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of the main units of an embodiment of theapparatus according to the invention,

FIG. 2 is a diagrammatic view of a simpler embodiment of the apparatusaccording to the invention with the main components thereof,

FIG. 3 is a diagrammatic view of the structure of the evaluation chain,

FIGS. 4 and 4a show a flow chart of the implemented processing steps,

FIGS. 5 and 6 are spectral representations of electromagnetic signalsdetected with the apparatus according to the invention, with frequencycomponents which are characteristic of the vital functions of humanliving bodies,

FIG. 7 shows a diode direct receiver without converter connectedupstream thereof,

FIG. 8a shows a circuit diagram of an analog high pass filter and ananti-aliasing filter in the form of a low pass filter,

FIG. 8b shows a circuit diagram of voltage symmetrising,

FIG. 9 is a view of a first embodiment according to the invention formonitoring vital functions, viewed from the side,

FIG. 10 is a view of the head of the embodiment illustrated in FIG. 9,from below,

FIG. 11 shows a second embodiment according to the invention forstationary mounting, viewed from the side,

FIG. 12 is a sectional view taken along line A--A in FIG. 11 through thesecond embodiment according to the invention,

FIG. 13 shows a third embodiment according to the invention for roommonitoring,

FIG. 14 shows an alternative of the arrangement shown in FIG. 13 formonitoring a plurality of building storeys,

FIG. 15 shows a further arrangement for room and/or building monitoring,and

FIG. 16 shows a still further arrangement for room monitoring andmonitoring the area in front of buildings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is firstly described hereinafter more generally and thenin greater detail with reference to individual embodiments.

FIG. 1 shows an arrangement with a transmitter 1 and a transmissionantenna 2 which transmit at a fixed frequency which is preferably in therange of some 100 MHz through about 10 GHz.

The transmission antenna 2 preferably has a lobe-shaped fixeddirectional characteristic. Depending on the respective embodiment ofthe invention the transmitter 1 and the antenna 2 are in the form of aportable unit or are mounted stationary.

The receiver device which is generally identified by reference 3 andwhich is shown in a simpler embodiment in FIG. 2 includes a receivingantenna 4 connected to a direct demodulator 5 which, from the receivedelectromagnetic signal, demodulates the frequency components which arecharacteristic of living bodies. That demodulation effect is performedin the form of phase or frequency demodulation and can already providethe desired frequency components at the output of the direct demodulator5.

In comparison with the embodiment of the direct demodulator shown inFIG. 7, it may also comprise a rectifier bridge of known kind whichresults in a voltage-doubled or voltage-multiplied useful signal.

In a further configuration, the receiving device 3 includes a frequencyconversion device 6 which is connected upstream of the demodulator 5 andwhich as a converter converts signals received above about 200 megahertzto terahertz into frequency ranges in which the direct demodulator 5 hasincreased reception powers. When using diodes, a bipolar or a fieldeffect transistor, that suitable, downwardly converted optimum workingrange is at about 100 kHz through 200 MHz.

Connected downstream of the direct demodulator is a filter device 7 forfiltering out undesired signal components, which limits the band widthof the electromagnetic signal, prior to the sampling operation (prior tothe analog/digital conversion operation), towards high frequencies. Thatfilter device 7 also limits the band width towards low frequencies. Theamplifier 8 connected downstream of the filter 7 increases the voltageor in an alternative configuration the current of the received signalsand passes it for sampling to an analog/digital converter 9.

After analog/digital conversion the frequency components which arecharacteristic of living bodies are processed by a computer device 10for spectral analysis and spectrally represented. In that case theintensity of the frequency components which are characteristic of livingbodies gives information about the presence of the vital functions ofthe human bodies detected.

In the event of evaluation of the signals in respect of time, thedigital signal, for removing distortion thereof, is folded or convolutedwith the inverse transfer function of the receiving device 3.

As reliable detection of those signals is extremely difficult, thedirect receiver with the non-linear element will be describedhereinafter, on the basis of a diode direct receiver.

Diode direct receiver

The reflected signal is phase or frequency modulated. Detection of thatmodulation is not possible, or is possible only with extremedifficulties, with the usual reception procedures for FM (frequencymodulation) and PM (phase modulation). So that a signal which is phasemodulated with 0.2 Hz can be detected, for example with 10 GHz,accurately to 0.2±0.02 Hz, short term-stable synchronised oscillatorswith deviations of less than 10⁻¹² would be necessary. That seemedhitherto unattainable from a technical point of view.

A way of directly detecting the modulation of the received signal wastherefore sought.

Suitable for that purpose are for example components with mostlyquadratic characteristics; they are inter aha field effect transistors,components with exponential characteristics which in a portion-wisemanner can be approximated as quadratic, diodes and transistors. If nowthe sum of two frequencies is applied as the impressed, receivedvoltage, that results in higher-order terms.

If there is a quadratic term, difference frequencies also occur, besidethe rectified current. In order to demodulate the phase-modulated signalwhich is reflected by the person to be detected, a conventionalrectifier can thus already surprisingly be used, in spite of the veryhigh requirements in regard to frequency behaviour.

The phase-modulated signal is impressed on the non-linearcharacteristic, and that results in currents which are proportional tothe phase modulation frequency Ω and the multiples thereof k*Ω. Thecurve shape of the modulation is not retained, in consideration of thedemodulation principle, but it has been found that those changes in thecurve shape are not critical for most uses according to the invention asdetection of the modulation can be sufficient for such uses.

The signal-noise ratio determines the sensitivity limit, in the case ofdirect detection. For the respiration rate, SN values of over 46 dB wereachieved, while for the heart rate, values of 26 dB were achieved at adistance of 3 mm and with oscillator powers of about 5 nW.

On the assumption that the heart emits spherical waves, between thetransmission and reception powers, there is a relationship which isinversely proportional to the second power of the distance. Therefore,for the ratio of the amplitudes of the respiration rate UA to the noiseUN or the heart rate UH to the noise, it is possible to estimate thatthe reception limit with a transmission power of 1 W is then at about 50m in relation to the heartbeat and at typically 160 m in relation torespiration.

Antennae with a higher gain and low-noise components can correspondinglyincrease those values in accordance with the invention. That means thatsufficient reception signals are still to be expected in the locationoperation, even for ground layers of several meters thickness.

The diode which is ideal in terms of saturation current IO andtemperature voltage is the Si power diode IN4004 whose suitability as arectifier is however limited to high frequencies due to the high barrierlayer capacitance. After that follows the low-signal Si diode IN4148,then the Si Schottky diode BAT46 and finally the two Ge diodes AA116 andAA144.

A diode direct receiver was respectively adjusted for 440 MHz 1.3 GHz,2.4 GHz, 5.6 GHz and 10 GHz. For 4 of the 5 frequencies, receivingantennae were designed with a direct diode receiver:

440 MHz: half-wave dipole with v=0.940, Z=60.5 Ω and BAT 46

1.3 GHz: half-wave dipole with v=0.906, Z=57.4 Ω and BAT 46

2.4 GHz: half-wave dipole with v=9.40, Z=60.5 Ω and BAT 46

5.6 GHz: full-wave multi-wire triadic dipole with v=0.73, Z=140 Ω andBAT 46.

It was already found with that receiver that the level of sensitivityfell greatly, relative to the 2.4 GHz receiver. At 10 GHz, it was nolonger possible to detect a usable voltage so that the construction of a10 GHz diode direct receiver was abandoned. The available diodes nolonger exhibited any usable rectifier effect at high frequencies of thatkind.

As signals according to the invention can be graded by experts as beingbelow the measurement limit, great attention has been paid to the typesof antenna used.

Antennae

The front-back ratio must be made as large as possible, for the locationprocedure, in order to receive signals which are incident in oppositerelationship to the main emission direction. Secondary lobes must alsobe minimized for that reason. Therefore the entire radiation diagramshould have a main lobe which is as narrow as possible and no secondarylobes.

The input impedance of the antennae can and should be adapted inaccordance with the invention to real or complex impedances in such away that power adaptation is achieved in the case of transmitters andnoise adaptation is achieved in the case of receivers. The fulfillmentof those requirements by an antenna design is however not possible atthe same time.

All antennae used are endfire antennae because backfire antennae ofcomparable dimensions always have a worse front-back ratio because thewaveguide structure must be excited in the rearward direction. Theantennae should be as wide-band as possible as an adjusting operationshould not be involved. Logarithmically periodic structures are known aswide-band antennae with a very good front-back ratio. A wide-band natureon the one hand and a pronounced directional effect on the other handare achieved by virtue of the logarithmic gradation of the waveguidestructures. The fact that the gain, compared to resonant antennae ofcomparable dimensions, is lower, is generally not a problem for thesituation of use according to the invention.

The polycone antenna can replace the rotational paraboloid antenna asdeviations from the paraboloid configuration which are less than a tenthof a wavelength do not have an adverse effect on the performance of theantenna. Even at a fifth of the wavelength, the loss of amplification isbelow 2 dB and can thus be disregarded for most cases.

The design configuration of the paraboloid reflector, which istechnically difficult to achieve, can thus be replaced by the polyconereflector which is easier to produce, without suffering disadvantages.The feed is however comparably expensive and complicated and thefront-back ratio is only improved with reflectors which are largerelative to the wavelength and whose illumination is limited to theinner region.

In order to overcome the problems involved in polarisation, in ourembodiments with the two higher frequencies (5.6 GHz and 10.368 GHz) acircularly polarised antenna was used in each case, on the one hand asthe receiving antenna and on the other hand as the transmitting antenna.Although admittedly that certainly gave rise to losses of typically 3dB, they however are small in comparison with the losses which can occurin the case of mutually rotated, linearly polarised antennae.

In one embodiment with only one common transmitting/receiving antenna,the incoming and outgoing waves could be successfully separated, bymeans of a circulator.

Particular attention is also paid to the high-frequency units, inconsideration of the difficult conditions to be overcome in terms ofmeasurement procedure.

High-frequency units

The high-frequency units required are set forth hereinafter. Thearrangement takes account of the possible links which occur between themodules and the peripheral elements. They correspond to theconfigurations according to the invention which we designed.

The direct modulators are used at the higher frequencies, that is to sayat frequencies above about 200 MHz, after the converters which convertto the intermediate frequency of 137.5 MHz. Both the diodes used andalso the transistors are operational at that frequency.

1. Diode mixer

The diode mixer comprises a symmetrical voltage multiplication circuitwith a resonance circuit at the input and a low pass filter at theoutput.

Here, in contrast to the voltage which can be achieved when using adiode as the direct receiver, it is possible to achieve the quadrupleoutput voltage as the sources are now connected in series. The increasedinternal resistance which is caused thereby is immaterial in terms offunction.

In practical operation it was found that the diode mixer is superior, inregard to the signal-noise ratio, to the other known mixer designs.

Low-frequency units

All modules which are operated in the low-frequency range are equippedwith their own power supply. That purpose is served by using individuallead accumulators of 12 V/2Ah which are provided with a voltagemonitoring circuit and an on switch. Strict separation of all powersupply units was found to be necessary as the use of a mains unitalready resulted in considerable interference and trouble.

The entire arrangement is thus completely insulated on the transmitterside and on the receiver side it is only connected to the mains by wayof the personal computer which however is in the form of abattery-powered unit in the case of portable apparatuses.

1. Pre-amplifier

The pre-amplifier uses a low-noise quadruple operational amplifier. Oneof the amplifiers is connected as an operating voltage symmetrisingmeans; the other three are connected as band pass filters and arecoupled together by way of high pass filters.

A low pass filter limits the noise of the first stage. By means of anoptional resistor, it was possible for the diode direct receiver to besupplied with a preconduction current from the pre-amplifier. Overalltwo pre-amplifier modules with different levels of gain were used. Asthe sensitivity of the entire arrangement can result in overdriving ofthe A/D converter and thus a data loss, a regulated amplifier isnecessary.

2. Sampling filter (anti-aliasing filter)

Sampling of time-dependent signals must be effected at a frequency whichis greater than twice as high as the highest frequency contained in theinput signal. Therefore the input signal must be spectrally limitedprior to the analog-digital conversion step. Astonishingly, for thepurposes of the present invention, that limitation operation must beeffected by an analog filter and cannot be replaced by digitalprocessing. If that is not taken into consideration, the situationinvolves sub-sampling of the spectral components which are above halfthe sampling frequency. They are mixed into the lower frequency rangeand irreversibly falsify the signal and therefore the success accordingto the invention cannot be achieved.

So-called digital anti-aliasing filters which lead the user to believethat band limitation can be effected after the A/D converter aresurprisingly found to be completely ineffective in regard to the probleminvolved; all errors linked to sub-sampling occurred. Subsequent digitalcorrection was no longer possible because of the destroyed signalcontent.

In general it is to be noted that among men skilled in the art, inregard to analog and digital parameters, there are false ideas such thatthe design of a measurement system for digital processing of analogparameters on the basis of the specifications of manufacturers and theexclusive use of the hardware and software offered thereby could notachieve the aim involved.

The requirements which are made in respect of the analog anti-aliasinglow-pass filter are very high, depending on the respective furtherprocessing involved. Thus the dynamic range must be at least 1 bitbetter than that of the subsequent A/D converter and likewise linear andnon-linear distortion effects must be at least 1 bit better than the A/Dconverter. Although the dynamic range of an N-bit A/D converter inpractice is mostly only N-2 bits, those relationships must be borne inmind. The use of switch capacitor filters is possible if the samplingtheorem is also taken into consideration in that respect and the dynamicrange achieved is sufficient.

Folding or convolution of the input signal with the sampling filterresults in amplitude and phase distortions and envelope curvedistortions, on the basis of the group transit or delay time of thefilter. Those signal changes can be taken into consideration if requiredby a procedure whereby the inverse transfer function of the samplingfilter is folded or convoluted with the sampled signal in the computer.That procedure is possible only if sampling was effected correctly. Incontrast in the event of sub-sampling the error is further increased.

Between the upper signal frequency fs, the sampling frequency fa, theasymptotic steepness or order of the sampling filter N and theover-sampling factor k, there is the following relationship, in relationto the achievable degree of accuracy or resolution A in bits: ##EQU1##

For a limit frequency of fs=2 Hz with a degree of resolution of A=13bits, that gives for example the following possible configurations:

    First-order filter (N=1)→sampling frequency fa=16384 Hz

    Third-order filter (N=3)→sampling frequency fa=64 Hz

    Sixth-order filter (N=6)→sampling frequency fa=16 Hz.

The last combination is the arrangement used in our embodiments. In thecase of low-order filters with `good-natured` performance in respect ofthe transfer function, we must surprisingly reckon on extremeover-sampling rates in order to attain usable results. In spite of thehigh sampling frequency of over 16 kHz, only the spectral components upto 2 Hz are correctly sampled (at A=16 bits, fs=20 kHz and fa=44 kHzfilters of the 109th order would be necessary in order to effectsampling in accordance with the sampling theorem).

Over-sampling has a further advantage: even if each analog-digitalconverter is ideal in respect of its characteristic, it adds thequantisation noise to the signal to be sampled so that the signal isfalsified not only by the quantisation operation, that is to saydiscretisation of the amplitude values, but it is also additionallycaused to have noise.

The noise can approximately be considered as white so that, with alarger sampling band width, that is to say with over-samplingcorrespondingly less noise falls into the signal band width and thus thesignal-noise ratio of the converter but not the signal can beproportionally improved.

The 6th-order sampling low pass filter used is provided by the seriesconnection of two third-order low pass filters (asymptotic edgesteepness 18 dB/octave or 60 dB per decade). Each low pass filtercomprises an operational amplifier connected as a voltage follower, andan R-C-circuit.

The amplitude, phase and envelope curve distortions due to the frequencyand phase characteristics of all filters as well as the group delay ortransit times can be reversed by a procedure whereby the time functionis folded or convoluted with its inverse transfer function T-1 (w) ofthe preceding signal path T (w) and thus complete pole-zero locationcompensation is effected. That can be necessary if the original timesignal is to be reconstructed and therefore deformation of the timesignal by the converters and the elements of the transmission chain mustbe avoided. In a situation of use in which the significant detection ofa spectral line is required, it is possible to disregard that.

In the structure according to the invention, in one embodiment, the timesignal passes from the converter (receiving antenna) to the personalcomputer (A/D converter) through at least one fifteenth-order high passfilter and a twenty first-order low pass filter which arise out of theproduct of the transfer functions of the individual elements of themeasurement chain (direct mixer, pre-amplifier, 2*low-pass filter,2*high-pass filter, A/D converter).

If necessary the dynamic behaviour of the analog part of the electronicsystem can also be improved by units which directly effect pole-zerolocation compensation. By virtue thereof, it is possible to reducenoise, an unfavourable transmission characteristic can be improved, oroptimum transmission properties can be achieved, in accordance withgiven criteria.

3. High-pass filter

In accordance with the invention spectral limitation of the inputsignal, with respect to the low frequencies, is desirable for threereasons:

1. 1/f-noise

The amplitude of the 1/f noise increases reciprocally relative tofrequency. Therefore, with an increasing measurement time, noisecomponents occur at a lower and lower frequency and falsify the signalto be measured. The main sources for the 1/f noise are the transmissionoscillator, the converter oscillator and the operational amplifiers.

2. Slow movements

At a constant speed movements of the body to be detected result in aDoppler frequency shift and thus spectral components which can fall intothe frequency band to be investigated. A wide additional band occurs, inthe event of irregular movements. The slower the movements, the lowerthe frequency of the spectra which are then more and more difficult toseparate from noise components.

3. Evaluation time

In order to identify a spectral line of the frequency f, measurementmust be effected at least for a time t=l/f, that is to say, the lowerthe frequencies to be detected, the longer the period for whichmeasurements must be made. As it is not possible to guarantee that themeasurement time is an integral multiple of the spectral component whichis of interest, a leakage effect occurs in the Fourier analysis. Thatresults in spectral spreading. Therefore, when analysing lowfrequencies, it is necessary to observe a measurement time which is amultiple of the period duration, in which case the degree of accuracyincreases proportionally with the measurement time. With 10% errors inthe spectral resolution and 0.2 Hz lower frequency it is necessary toreckon on a measurement time of typically 50 seconds.

FIG. 3 shows the general structure of the evaluation chain. Personalcomputers from the office sector, IBM-PC-compatible type, are used ascentral units, as the power thereof is adequate for the task involved.

The plan shown in FIGS. 4 and 4a gives an overview of the implementedprocessing steps, therein F{ } denotes the Fourier transformation andF-1{ } denotes the inverse Fourier transformation.

RESULTS

After various preliminary tests a sampling rate of 16 Hz with a unipolarresolution of 13 bits (total resolution 14 bits) was found to be wellsuited. The window width selected for spectral analysis was 512 values,corresponding to about 33 seconds: the Hamming window was selected asthe window.

FIG. 5 shows the heart rate of a test person with respiration stopped.The spectral component stands out so clearly from the surroundings thatfurther processing is not necessary to detect the heartbeat of the testperson. The quantitative spectrum is plotted in any units, in relationto frequency in Hertz. Measurement was effected at 2.4 GHz, the diodedirect receiver, that is to say the 1/2-dipole, was used as thereceiver, the local oscillator was used as the transmitter, respirationwas stopped.

FIG. 6 shows the spectrum of the signal reflected by a breathing person,using the diode direct receiver and the logarithmic-periodic Yagiantenna and the 1.3 GHz transmitting oscillator as the source. Bothheart rate and also respiration rate are present At the frequency of 440MHz, the tests were found to be difficult, because of the extremesensitivity of the entire arrangement. Almost all test recordingsexhibited overdriving phenomena and reactions to external events.

The problem of overdriving can be resolved by suitable attenuation;detection of respiration and cardiac activity is not influenced thereby.

If a circulator is used, then, as described, it is possible just to usean antenna which transmits and receives simultaneously.

The examples clearly demonstrate that the detection of living people ispossible. In that respect neither walls nor distances of some 10 metersare an obstacle worth mentioning. Working frequencies of 1.3 GHz and 2.4GHz were found to be highly suitable. When using antennae which arestill manageable, the level of sensitivity is sufficiently high toachieve reproducible results with clear identification of the heartbeatand respiration without intensive numerical processing steps beingnecessary, as suitably strong reception signals are already present.

Circuit diagram high-pass and anti-aliasing low-pass filters

The circuit diagram of the unit employed for band restriction is shownin FIGS. 8a and 8b. The third-order high pass filter suppresses thelow-frequency noise components, in particular the 1/f noise. Thefollowing third-order low-pass filter limits the spectrum to higherfrequencies. There then follows a linear amplifier stage for levelmatching. The operating voltage is electronically symmetrised so that aunipolar supply is sufficient. Two of those units in cascaderelationship fulfil the requirements set by the sampling theorem.

Diode demodulator circuit diagram

A diode detector whose circuitry is shown in FIG. 7 serves for phasedemodulation of the reception signal which is mixed on to theintermediate frequency and as a direct demodulator for the developedreceiver antennae. The circuitry corresponds to a typical power meter; apre-conduction or input current can be impressed from the output. Theinput impedance can be adapted to the IF-mixer or the antennae.

Diode direct receiver circuit diagram

The diode direct receivers comprise diode detectors which are 1/2 or 1wavelength long and which are multiplied by the corresponding shorteningfactor and are suitably connected upstream. A pre-conduction or inputcurrent can be impressed at the output.

In addition each unit is provided with its own stabilised voltage supplyand its own on-off switch so that units with a long time constant (localoscillators, pre-amplifiers, low-pass filter) could be operated incontinuous duty and were in thermal and electrical equilibrium whileconsumers or loads with a high current consumption (final transmittingstages, converters) can be switched off between uses.

Preferred embodiments of the invention are described hereinafter.

A first embodiment according to the invention includes a system formonitoring the vital function of respiration and/or heartbeat in themedical sector. Disposed in a housing 14 are the transmission antenna 2and the receiving antenna 4 with their respective associated reflectors.The antenna 2 which is used as the transmission antenna is connected toa transmitter 1 which outputs a power of 20 mW as a substitute orequivalent load of real 377 Ω.

The horizontal and vertical aperture angles of the antennae are adaptedto the respective use involved. For monitoring in intensive care units,at least the reception antenna has a reception characteristic which hassmall secondary lobes and whose main detection area is approximately ofthe size of a human thorax. The receiving antenna 4, Rx is connected toa receiver which, by means of the converter 6, converts the incomingsignals into the above-described frequency range. That is then followedby the demodulator 5, the amplifier, the filter 7 and a driver forsignal transmission.

The signals are fed to the remotely disposed analog/digital converter 9by means of the screened lines (not shown). The analog/digital converter9 and the further above-described electronic evaluation system aredisposed either in a portable unit, preferably in a small suitcase, orin a static mains-powered item of equipment, or they are part of acentral monitoring unit with central display of the vital functions inthe form of the spectra shown in FIGS. 5 and 6, in a clinical monitoringstation. In order to make the signals correctly evaluatable in the timeregion, convolution is effected with the inverse transfer function ofthe signal path which is disposed upstream of the analog/digitalconversion operation. Thus, the substantially instantaneous condition ofthe vital functions or, with suitable image storage devices, the historythereof, can be represented on monitors of the central monitoringstation or the portable unit.

In a simpler embodiment as shown in FIG. 10 the front plate 15 carriesan on/off switch 16 and an optical indicator 17 and/or an acousticindicator 18. The optical indicator 17 can be arranged beneath atransparent part of the front panel 15, as shown in FIG. 10, or abovethe housing 15, as shown in FIG. 9. By means of a clamping connection 19which is only diagrammatically shown in FIG. 9 in the form of a screwclamping device, this first embodiment according to the invention can bequickly and easily fixed to or in the vicinity of beds of patients whoare to be monitored. Moreover, it is in accordance with the inventionfor the fixing device 19 used to be any other known alternativeconstructions such as for example mechanical coupling arrangements or abayonet arrangement with the respective stationarily mountedco-operating member. In that way, the apparatus can be fixed to or inthe vicinity of the bed of the person to be monitored, in an at-homesituation.

A hinge arm 21 together with the rotary pivot joint 22 at the end of thearm 21 permits controlled orientation of the apparatus in per se knownmanner.

In a further embodiment as illustrated in FIG. 11, the housing 15 isfixed approximately centrally with a pull or tie device 23 to a ceiling24 of a building. The device 23 permits adjusting in respect of heightand in particular permits the housing 15 to be moved downwardly so thata person lying under the apparatus can be detected in the optimumfashion, while when the apparatus is displaced upwardly, there is noimpediment in terms of freedom of movement.

In order reliably to take account of the clinical factors involved, thedetected band width of the frequencies is limited to a range of 0.02 Hzthrough 6 Hz. In that way, respiration periods of 166 ms through 50 sand pulse rates of 1.2 through 360 beats per minute can be detected. Anelectronic evaluation system disposed at a downstream location detectsthe height of the spectrally limited signal and has a threshold valuesetting which, in the event of the absence of the signals which providewarning for the vital functions, sets off an optical and/or acousticalarm or which, upon being integrated into a monitoring system,transmits the alarm condition to that system.

In another alternative configuration the detectable respiration periodsare limited to less than 30 s so that the period to evaluation of thesignals is also not longer than somewhat over 30 s.

The main areas of use of the above-described embodiments concern themonitoring of people who are in danger of committing suicide, cable-freemonitoring of comatose people and people with burns injuries. Inclinical situations and at home, it is possible to provide formonitoring people who are in need of care and who are in need ofintensive care, while in relation to small children, it is possible toprovide for monitoring in regard to the absence of the vital functions,in order to prevent sudden death of the child. Sleep disturbances whichare known from intensive care units and which are caused by the cablearrangements can be alleviated and in part even eliminated as, besidesthe purely mechanical obstruction and hindrance, the psychologicalstrain also decreases.

It is also possible to detect the cardiac rate of the unborn child, inthe case of pregnancy investigations. That also makes it possible toprovide for trouble-free and uninterrupted continuous monitoring,without the electrodes which conventionally have to be fitted.

In a further embodiment according to the invention, as shown in FIG. 13,a room 25 is monitored by means of a transmitting/receiving devicedisposed in one corner of the ceiling. As described in connection withthe preceding embodiments, the transmission antenna 2 and the receivingantenna 4 are connected to the above-described electronic units forsignal evaluation purposes.

The transmitter 1 preferably transmits in the frequency range of between300 MHz and 3 GHz, and it outputs a power of between some mW and severalW at a substitute or equivalent load of real 50 Ω or real 377 Ω. In thecase of room monitoring the antennae 2, 4 are in the form of tripoleprisms, as shown in FIG. 13.

In the further embodiment shown in FIG. 14, a circularly polarisingtransmitting/receiving antenna 2, 4 is arranged in the top floor 26 ofthe building 27. By virtue of the appropriate configuration of thespatial transmission characteristic of the transmitting antenna 2 andthe spatial receiving characteristic of the antenna 4, they are adaptedto the desired detection area, in general the dimensions of the buildingto be monitored. It is also possible to arrange a plurality oftransmitting antennae 2 and a plurality of receiving antennae 4 in theregions to be monitored, and for each to be connected to the electronicevaluation system.

In the embodiment shown in FIG. 15 the transmitting or the receivingantenna 2, 4 are arranged behind a suspended ceiling 28. The large-areaextent of the antennae simplifies accurate definition of the detectionarea. FIG. 15 also shows a further concealed monitoring arrangement, inthe region of the side wall 29.

FIG. 16, in addition to monitoring of the room 30, also shows atransmitting/receiving antenna combination 2, 4 for monitoring the areain front of a building. In this case the region 30 which is onlydiagrammatically illustrated can be a forecourt of a private and apublic building. Thus for example uninterrupted monitoring, such as tocover an entire surface, is possible in a psychiatry situation or in apenal detention situation. In addition, a subsequently connectedelectronic evaluation system can perform automatic signalling, asdescribed hereinbefore in regard to the medical areas of use.

Further important areas of use are in the sector of the chemicalindustry and in relation to installations, which are exposed toradiation, of the nuclear energy suppliers or nuclear fuel producers andprocessors. Regions which are exposed to radiation or the effects ofchemicals can be monitored in such a way that an entire surface iscovered thereby, so that people can enter those areas, withouttriggering an alarm, only if they have been suitably made known, or, inthe event of dangerous substances escaping, the presence of livingpeople in the vicinity of the location at which the substances haveescaped can be detected.

A further essential use lies in the area of combatting fire in acontrolled and specific manner. Wherever oxygen-binding extinguishingagents or special extinguishing procedures for combatting fire are usedinstead of conventional agents or procedures in order to avoid majorproperty damage (for example in the case of a fire in the printing andcomputer industry), then, in order not to endanger the lives of peoplestill in the buildings, the fire-extinguishing procedure may begin onlywhen the locations of the fire have been checked to ascertain whetherliving people are present there. That monitoring effect is prescribed bystatute law for the use of specific fire-extinguishing agents, but it ishighly controversial, because of the disadvantages that it involves inregard to life and limb of the fire services. Checking of the firelocations for any people who may still be alive on the other hand can beeffected efficiently, speedily and from the exterior, that is to sayalso from outside the premises which are on fire.

Thus, any people in the premises which are on fire are detected morequickly, rescued more speedily and the fire services are less in dangerat the source of the fire. The extent of fire damage can additionally begenerally minimised by virtue of the fire-extinguishing procedurebeginning are quickly.

I claim:
 1. Apparatus for detecting vital functions of living bodies bydetecting electromagnetic signals comprising a receiving device forreceiving electromagnetic signals from living bodies, wherein thereceiving device (3) for receiving electromagnetic signals includes adevice for obtaining frequency components that are characteristic of theliving bodies, out of the received electromagnetic signals, wherein thereceiving device (3) includes a direct demodulator (5) that has anon-linear current/voltage characteristic that is frequency-selectivefor demodulation of frequency components that are characteristic of theliving bodies.
 2. Apparatus as set forth in claim 1 characterized inthat the direct demodulator demodulates frequency components which arecharacteristic of vital functions of living bodies directly out of thereceived electromagnetic signals.
 3. Apparatus as set forth in claim 2characterized in that the direct demodulator (3) includes one of adiode, a bipolar and a field effect transistor as thefrequency-selective element.
 4. Apparatus as set forth in claim 1characterized in that the receiving device (3) includes a frequencyconversion device (6) connected ahead of the demodulator (5) in adirection in which the electromagnetic signals are received. 5.Apparatus as set forth in claim 1 characterized in that the apparatusincludes a transmission device (1) transmitting of an electromagneticcarrier signal at a fixed frequency.
 6. Apparatus as set forth in claim5 characterized in that the carrier signal is in a frequency range ofapproximately one MHz to approximately one THz.
 7. Apparatus as setforth in claim 1 characterized in that the device for obtainingfrequency components which are characteristic of the living bodiesincludes a filter device (7), a sampling device, an A/D converter (9)and a computing device (10) for spectral analysis.
 8. Apparatus as setforth in claim 7 characterised in that the filter device (7) includes atleast one analog sampling filter.
 9. Apparatus as set forth in claim 8characterised in that the sampling filter limits the band width of theelectromagnetic signal towards high frequencies prior to the samplingoperation and prior to the A/D conversion operation.
 10. Apparatus asset forth in claim 1 characterized in that the apparatus furtherincludes a transmission antenna (2) for transmitting an electromagneticcarrier signal, and the receiving device comprises a receiving antenna(4) wherein the transmission and receiving antenna are held in a commonhousing (14) for pivoting and nutating movement with a releasablyfixable holder (19).
 11. Apparatus as set forth in claim 1 characterizedin that the apparatus further includes a transmission antenna (2) fortransmitting an electromagnetic carrier signal and the receiving devicecomprises a receiving antenna (4) wherein the transmission and receivingantenna are mounted in a common housing (14) which is fixed to a ceiling(24) by way of a holder (23) which is adjustable in respect of height.12. Use of an apparatus as set forth in claim 1 further includingpositioning means for positioning the apparatus to allow forcontact-free monitoring of the vital functions of intensive carepatients.
 13. Use of an apparatus as set forth in claim 1 furtherincluding positioning means for positioning the apparatus to allow formonitoring one of small children and apnoea patients for at least one ofcardiac and respiratory arrest.
 14. Use of an apparatus as set forth inclaim 1 further including positioning means for positioning theapparatus to allow for monitoring the state of inmates in places ofdetention.
 15. Use of an apparatus as set forth in claim 1 furtherincluding positioning means for positioning the apparatus to allow forat least one of monitoring and safeguarding at least one of rooms,buildings and open land surrounding same.
 16. A method for detectingvital functions of living bodies by detecting electromagnetic signalscomprising receiving electromagnetic signals from living bodies andobtaining frequency components which are characteristic of the livingbodies from the received electromagnetic signals by directlydemodulating the received electromagnetic signals by a directdemodulator having a non-linear current/voltage characteristic that isfrequency-selective for demodulation of frequency components that arecharacteristic of the living bodies.
 17. The method as set forth inclaim 16 further characterized by converting the receivedelectromagnetic signals to an intermediate frequency between high andlow frequencies.
 18. The method as set forth in claim 16 furthercharacterized by limiting the received electromagnetic signals with ananalog device towards high and low frequencies.
 19. The method as setforth in claim 18 further characterized by transforming the digitalsignals from a time region into a frequency region and then evaluatingand representing the digital signals as output signals.
 20. The methodas set forth in claim 19 further characterized by analyzing thetransformed signals in a frequency range of from about 0.01 Hz throughabout 10 Hz for frequency components of at least one of cardiac andrespiratory activity, which are characteristic of vital functions ofliving bodies.
 21. The method as set forth in claim 20 furthercharacterized by analyzing the transformed signals in a frequency rangebetween about 0.02 Hz and about 3 Hz.
 22. The method as set forth inclaim 16 further characterized by filtering, sampling, and convertingthe received electromagnetic signals into digital signals.
 23. Themethod according to claim 22 further characterized by folding thedigital signals with a window function in a time region and with aninverse transfer function of a receiving device.
 24. The method as setforth in claim 16 wherein the step of obtaining frequency componentswhich are characteristic of the living bodies further includescontact-free monitoring of the vital functions of intensive carepatients.
 25. The method as set forth in claim 16 wherein the step ofobtaining frequency components which are characteristic of the livingbodies further includes monitoring at least one of small children andapnea patients for at least one of cardiac and respiratory arrest. 26.The method as set forth in claim 16 wherein the step of obtainingfrequency components which are characteristic of the living bodiesfurther includes monitoring the state of inmates in places of detention.27. The method as set forth in claim 16 wherein the step of obtainingfrequency components which are characteristic of the living bodiesfurther includes at least one of monitoring and safeguarding at leastone of rooms, buildings, and open land surrounding same.